Human beings do not perceive sounds in the same way in the air and in water. However for obvious reasons of safety, the wearer of the watch must be able to be warned in an optimum manner whatever medium (air or water) he is in. This is particularly true when the wearer of the watch makes a submarine dive. It is vital that the diver is warned in sufficient time that his dive time is running out or that he has reached his maximum dive depth.
Diving watches are known from Japanese Patent Nos. JP 60-001588 and JP 07-333359 in the name of Seiko and JP 57-101786 in the name of Casio.
The electronic watch disclosed in JP Patent No. 60-001588 is capable of generating an acoustic time alarm and an acoustic depth alarm. The audible signal frequency is the same for both alarms. However, the features of the alarm (repetition frequency, sound length) are different depending upon whether it is the time alarm or the depth alarm.
The electronic watch disclosed in JP Patent No. 57-101786 includes a device that indicates the depth reached and generates an acoustic signal when this depth reaches a predetermined value.
The electronic watch disclosed in JP Patent No. 07-333359 includes means that detect whether the depth measurement has reached a predetermined value. An acoustic alarm is then produced and a hand is actuated.
The three aforecited documents all provide the possibility of producing an acoustic alarm when the wearer is making a submarine dive. However, none of these three documents discloses or suggests adapting the frequency of the alarm as a function of the medium (air or water) in which the user is located. It has been observed that the medium (air or water) in which the acoustic signal propagates and the auditory apparatus (external/internal ear or the bones of the cranial cavity in the case of submarine perception) act like filters as regards the signal. They form what is currently called a perception filter. An empirical curve can be obtained, which, depending upon the medium in which one is situated, indicates, for a given frequency, the difference between the acoustic power emitted and the acoustic power as it is perceived by the user. It will thus be noted that in the air, the sound perceived by the user is only very slightly attenuated by the perception filter in a broad frequency range comprised between 1 and 10 kHz. In water, sound transmission seems optimal at a frequency of the order of 800-1000 Hz with attenuation of the order of 40 dB. However, at a frequency two times higher, attenuation is greater than 60 dB.
It is thus an object of the present invention to provide a portable object such as a diving watch including a sound generator device which provides the user thereof with optimum sound perception whatever the medium in which the user is situated.